1. Field of the Invention
The present invention relates to a sheet feeding apparatus which suctions and conveys sheets by blowing air on a sheet bundle to separate from one another, and the present invention also relates to an image forming apparatus having the sheet feeding apparatus.
2. Description of the Related Art
In the related art, such an image forming apparatus, for example, a printer or a copying machine, which has a sheet feeding apparatus for conveying sheets by feeding one by one from a sheet storage case, has been known. In recent years, a sheet feeding apparatus of a so-called air feeding type has been proposed in order to realize a high-speed conveyance of sheets, in which a gas (mainly air) is blown on the end of a sheet bundle to float up several sheets to separate from one another, and convey the separated sheet by suctioning it to a suction conveyance belt. The technique is described in U.S. Patent Application Publication No. 2005/206068 A1.
Herein, an exemplary sheet feeding apparatus of the air feeding type will be described with reference to FIG. 18A to FIG. 20B. FIG. 18A is a schematic side view illustrating a conventional sheet feeding apparatus; FIG. 18B is a schematic plan view illustrating the conventional sheet feeding apparatus; and FIGS. 19A and 20B are views each illustrating a sheet feeding operation of the conventional sheet feeding apparatus.
As illustrated in FIG. 18A, a sheet storage portion (storage case) 11 of a sheet feeding apparatus includes a sheet tray 12 on which a sheet bundle is stacked. The sheet storage portion 11 also includes a back end regulating member 13 configured to regulate a back end side of the sheets in a sheet conveying direction, the sheets being stacked on the sheet tray 12, and side end regulating members 14, 16 configured to regulate a width direction of the sheets perpendicular to the sheet conveying direction. The sheet storage portion 11 is configured to be drawn out toward a front side in the drawing by means of a slide rail 15 so as to enable sheets to be added, drawing out the sheet storage portion 11.
As illustrated in FIG. 18B, the back end regulating member 13 and the side end regulating members 14, 16 are configured to be adjustable in position in directions of arrows Q, R in the drawing, according to a size of sheet 35 (the maximum L: indicated by a dashed-two dotted line in the drawing, the minimum S: indicated by a dashed-dotted line in the drawing). The back end regulating member 13 and the side end regulating members 14, 16 need to regulate sheets in various sizes, so that the sheet tray 12 has a shape indicated as a shaded area in the drawing.
A feeding operation of the sheet feeding apparatus of the air feeding type will be described next with reference to FIGS. 19A and 20B. In a state illustrated in FIG. 19A, when a user retracts the sheet storage portion 11 after drawing it out to set the sheets therein, the sheet tray 12 starts to lift in a direction of arrow A in the drawing by means of a driving portion (not illustrated). The sheet tray 12 is then stopped in a position in which a distance from a suction conveyance belt 21 reaches size B, and waits for a feeing signal.
In a state illustrated in FIG. 19B, upon detection of the feeding signal, a loosening and separating air supplying portion 31 is activated to absorb air in a direction of arrow C in the drawing. This absorbed air is passed through a separating duct 32 and is then blown on sheets 35 (hereinafter, also referred to as a sheet bundle 35) through a loosening nozzle 33 and a separating nozzle 34 in directions of arrow D and arrow E, respectively. The top several sheets (indicated by 35A) are blown up from the sheet bundle 35 on which the air has been blown. On the other hand, a suction fan 36 is activated to blow air in a direction of arrow F in the drawing. At this time, a suction shutter 37 is still closed. Further, the side end regulating portions 14, 16 are mounted with auxiliary separating fans 17, 18, respectively, and the air is blown from openings 14A, 16A to the top of the sheet bundle 35. Formation of the auxiliary separating fans 17, 18 further ensures blowing up of sheets, thereby certainly loosening them.
As illustrated in a state in FIG. 20A, the suction shutter 37 is rotated in a direction of arrow G when a predetermined time has elapsed from detection of the feeding signal and the blowing up of the sheets 35A becomes stable. Accordingly, suction force in a direction of arrow H in the drawing is generated from a number of suction holes (not illustrated), formed in the suction conveyance belt 21, so that the topmost sheet 35B is suctioned onto the suction conveyance belt 21.
As illustrated in a state in FIG. 20B, the topmost sheet 35B is conveyed in a direction of arrow K in the drawing by rotating belt driving rollers 41, 41 for supporting the suction conveyance belt 21, in a direction of arrow J in the drawing. Thereafter, a drawing roller 42 is rotated in directions of arrows M, P, in the drawing so that the topmost sheet is conveyed to a conveyance path on the downstream side.
Incidentally, if the back end regulating member or the side end regulating members for the sheets is not set in a proper position, a sheet feeding failure is caused. For example, as illustrated in FIG. 21A, if the loosening and separating air supplying portion 31 is activated with the back end regulating member 13 being set improperly, problems would be caused as follows. In a case where the air is blown on the sheet bundle 35 from the loosening nozzle 33 and the separating nozzle 34 through the separating duct 32, in directions of arrows D, E, respectively, as illustrated in FIG. 21B, the top several sheets (35A) of the sheet bundle 35 are shifted backward (toward the back end side). Therefore, even if the suction shutter 37 is rotated in a direction of arrow G as illustrated in FIG. 21C, the topmost sheet 35B is not suctioned onto the suction conveyance belt 21, thereby causing the feeding failure as illustrated in FIG. 21D.
Further, such a feeding failure is also caused like the above case if side end regulating members 14a, 14b are not properly set as illustrated in FIGS. 22A, 22B each illustrating the feet feeding apparatus as viewed from the top. More specifically, in a case where the air is blown on the sheet bundle 35 from the loosening nozzle 33 and the separating nozzle 34 through the separating duct 32, respectively, the top several sheets of the sheets 35 are laterally shifted as illustrated in FIG. 22C. Therefore, even if the suction shutter 37 is rotated in a direction of arrow G in FIG. 16, the topmost sheet 35B is not suctioned onto the suction conveyance belt 21, thereby leading to the feeding failure.
Herein, problems caused when the side end regulating members are not placed in proper positions will be described with reference to FIG. 19A. As illustrated in FIGS. 22A, 22B each illustrating the sheet feeding apparatus as viewed from the top, if the loosening and separating air supplying portion 31 is activated with the side end regulating members 14a, 14b being set improperly, problems would be caused as follows. More specifically, when the air is blown on the sheet bundle 35 from the loosening nozzle 33 and the separating nozzle 34 through the separating duct 32, respectively, the top several sheets of the sheet bundle 35 are laterally shifted as illustrated in FIG. 22C. Therefore, the topmost sheet 35B is not certainly suctioned onto the suction conveyance belt 21, thereby causing the feeding failure.
Further, in a case where the sheets are fed on the condition that the sheets stacked on the sheet tray 12 are prominently curled up, it could be difficult to carry out the normal feeding in some cases. More specifically, for example, a suction failure of sheets due to the curl on the sheet may lead to the feeding failure.